1. Field of the Invention
The present invention relates to an imaging apparatus such as a digital camera, particularly, to an imaging apparatus which conducts photographing by selecting the most suitable emission method from a plurality of emission methods based on a preliminary emission result.
2. Description of the Related Art
In an imaging apparatus such as a digital camera, photographing is conducted by using an illumination device such as a strobe light when a subject is dark. The following two methods are mainly used as an emission control method.
A first method is mainly adopted for a digital camera. The first method is a method of preliminary flashing a strobe light before photographing, measuring light volume from a subject by means of an imaging device, and setting the appropriate emission volume of the strobe light. In this emission control method, the preliminary emission is conducted before photographing, and the reflected light volume from the subject is measured by means of the imaging device, so as to calculate the appropriate main emission volume of the strobe light based on the brightness of the subject obtained by measuring the reflected light volume. In this case, using the property such that emission volume attenuates in inverse proportion to the squared distance to the subject, it is general to calculate the emission volume to the subject by measuring the distance to the subject with a measurement device, so as to use the calculated emission volume as the reference emission volume in the preliminary emission and the main emission. More particularly, in the preliminary emission, the emission is performed by the reference emission volume calculated according to the subject distance, and in the main emission, the emission volume is slightly adjusted such that the photometric result is reflected in the reference emission volume.
However, in the above emission control method, a measurement error in the subject directly appears as an error of the reference emission volume. In terms of focusing, it is not practically a problem to lower the measurement accuracy by the deepened depth of field for a long-distance subject. However, in terms of exposure control, it is unacceptable to lower the measurement accuracy because of the above reason (the property such that the emission volume attenuates in inverse proportion to the squared distance to the subject). If the measurement error is within a certain range, the emission volume of the main emission can be corrected by the photometric result in the preliminary emission. However, if the measurement error is increased, the emission volume of the main emission can not be corrected by the photometric result.
A second method is mainly adopted for a silver salt camera which conducts photographing by using a photographic film. This second method is a method of measuring reflected light from a subject by using a photometry device provided in the front face of the camera, and continuing emission till a predetermined light volume is obtained. In this method, a strobe light is measured during photographing, so the preliminary photometry is not necessary and also the time required for the photometry is omitted. However, accurate photometry may not be performed because of parallax, especially when the subject is a close-range subject
As described above, each of the first and second emission control methods has advantages and disadvantages. Accordingly, there is an apparatus which performs an emission control by switching the above two control methods according to a distance to a subject (refer to JP2527734B). This apparatus carries out an emission control which changes an aperture stop and shutter speed based on a distance to a subject, when the apparatus determines that the distance to the subject is shorter than a limit distance defined based on measurement accuracy. On the other hand, this apparatus carries out an emission control by means of modulated light based on the light volume of the reflected light from the subject, when the apparatus determines that the distance to the subject is longer than the limit distance.
Moreover, a stroboscopic photographing apparatus which determines the emission volume for photographing by a photometric result is disclosed in JP2006-53493A. In this apparatus, an amplification control device is controlled according to an output of a measurement device when measuring the preliminary emission, so as to vary amplification (receiving sensitivity) of imaging signals.
However, in the emission control method disclosed in JP2517734B, it is a premise that the measurement of the subject distance be accurately conducted. For example, when the measurement is not accurately conducted due to low brightness, the most suitable emission control can not be performed. In addition, when the measurement of the subject distance is performed by using a focusing control method such as CCDAF (Charge-Coupled Device Auto Focus), an approximate subject distance is calculated from a focused position of a focusing lens. Therefore, measurement accuracy more than a driving step of the focusing lens can not be obtained, and also sufficient measurement accuracy can not be obtained especially for a long-distance subject. In this case, the limit distance capable of obtaining sufficient accuracy in the CCDAF measurement can not be always used as a switching distance when switching the above two methods. For example, if the above emission control by the second method is conducted in the vicinity of the limit distance of the CCDAF measurement, accurate photometry is not conducted because of parallax.
Accordingly, there is a need for an imaging apparatus capable of conducting the most suitable emission control when a correct measurement result is not obtained.